The present invention relates to dual layer tablets for the treatment of water to enhance and improve the properties thereof. In a further aspect, the present invention relates to the methods of making the dual layer tablets and the uses thereof.
In a water system that includes recreational applications (i.e. pools or spas), industrial water applications (i.e. cooling towers) or household applications (i.e. bathroom toilets), the purification of the water and the system containing the water are usually done by using a wide variety of biocides, sanitizers, disinfectants, dispersants, or surfactants. All the products are either in a liquid or solid form.
One of the challenges for these types of products is that the tablets must have good tablet strength, good tablet quality and show no sign of fracture, swelling or breakage under normal storage conditions. The tablets must also readily dissolve and release the active ingredients to provide multifunctionality. These products should be capable of being designed to provide immediate treatment and slow and long lasting maintenance to the water system.
Another problem for the treatment of such water systems is associated with the fact that customers have to use and store many different chemicals to take care of just one system. An all-in-one type product is rarely available for consumers to use that would provide the desired multifunctionality and benefits. In recreational water treatment applications like swimming pools and spas, a fast dissolving solid (such as sodium dichloroisocyanuric acid, lithium hypochlorite or formulations thereof) are used to provide a dosage of the active oxidizer or sanitizer (i.e. source of hypochlorous acid) on contact with water. Likewise, the sanitizer is often a slow dissolving solid (such as trichloroisocyanuric acid, calcium hypochlorite, 1,3-dichloro-5,5-dimethylhydantoin, 1-bromo-3-chloro-5,5-dimethylhydantoin, 1,3-dichloro-5-ethyl-5-methylhydantoin or formulations thereof) to maintain a sanitizer residual for an extended period of time.
Similarly, algaestats and algaecides, which help prevent the buildup of algae or fungi, and water clarifiers, which help remove particles from water are typically added as separate products for the treatment of recirculating water systems. Similarly, in industrial water treatment, such as for cooling towers, sanitizers are specifically designed to kill microorganisms which lead to biofouling, biofilms and the like, where corrosion and scale inhibitors are added separately to reduce corrosion and scale in the system.
As a result, consumers or operators spend considerable time and resources to maintain a wide spectrum of chemicals and to determine when, why, and how much of these chemicals must be added to their water system. Hence, a product with multifunctionality would have great value in treating water that requires such chemical treatment, including toilet bowls, swimming pools, spas and industrial water applications. In addition, oxidizers or other chemicals that are added to these systems are often not compatible when commingled with each other and hence undesirable. In such instances, the activity of the oxidizer or sanitizer will diminish over time. Tableting separate layers of oxidizers or sanitizers overcomes the disadvantages outlined above. Also relevant to this invention is that different rates of dissolution for oxidizers and sanitizers as separate layers within a single tablet would be advantageous. A commingled blend with different oxidizers or sanitizers would not satisfy this need.
Multilayer tablets (specifically dual layer), ring/core and jacket/core tablets have been established in the prior art in the pharmaceutical and household uses, particularly for automatic dishwashing applications. The prior art in dual layer tablets has focused on releasing various active substances at different rates to ensure that both layers of the tablet are not dissolved simultaneously or for separating ingredients which are incompatible with one another.
Kruse, et al. (U.S. Pat. No. 4,828,749) discloses a dual layer tablet for dishwashing applications. The said composition is comprised of one layer of a metal silicate, metal triphosphate and surfactant while the second layer is comprised of a metal silicate, metal triphosphate and from 0.5 to 5% of an active halogen releasing compound such as trichloroisocyanuric acid (TCCA) or sodium dichloroisocyanuric acid (NaDCCA).
Chun, et al. (U.S. Pat. No. 5,133,892) discloses a multilayer tablet which separates a source of halogen bleach (from 0.1% to 20% by weight available chlorine) from a combination of a peroxygen bleach and an enzyme by means of a barrier.
Wäschenbach, et al. (U.S. Pat. No. 6,194,368) also discloses a dual layer tablet for dishwashing applications where an oxygen or chlorine containing bleach (present between 1% and 40% by weight) and a corrosion inhibitor is separated from a bleach activator.
Saslawski, et al. (U.S. Pat. No. 6,372,255) discloses a much broader application of multi-layered tablet technology relating to the instant and then prolonged release of active substances comprising of at least two superposed layers. However, the second layer of the tablet comprises a nonbiodegradable inert porous polymeric material in which the active material is dispersed.
The only prior art that applicants have uncovered which mentions the use of a contiguous dual layer tablet for treating recirculating water is disclosed by Kibbel and Hollenbach in U.S. Pat. No. 3,873,685. Kibbel, et al. discloses a process for producing a contiguous, layered tablet consisting of a fast dissolving layer of sodium dichloroisocyanuric acid dihydrate (NaDCCA·2H2O), and a slow dissolving layer of trichloroisocyanuric acid (TCCA).
Karbowski, et al. (U.S. Pat. No. 4,800,082) discloses a sustained release microbiological control composition in the form of tablets for aqueous industrial systems.
Lavatory cleaning blocks which release a halogen disinfecting agent in a controlled, substantially constant rate as shown in Hung, et al. (U.S. Pat. No. 5,178,787).
Farina, et al. (U.S. Pat. No. 5,603,941) discloses a compacted or tableted composition containing at least one biodispersant, at least one halogenated biocide and a halogen scavenger.
Secemski (U.S. Pat. No. 5,783,540) discloses tablets having at least two layers for dishwashing applications.
Another multilayered dishwashing tablet is shown by Gorlin, et al. (U.S. Pat. No. 5,962,387).
Detergent shaped bodies are described by Holderbaum, et al. (U.S. Pat. No. 6,251,848) wherein active substances are represented from one another as a core/jacket shaped body.